Detailed Description

template<typename T>
class drake::multibody::PrismaticSpring< T >

This ForceElement models a linear spring attached to a PrismaticJoint and applies a force to that joint according to.

  f = -k⋅(x - x₀)

where x₀ is the nominal (zero spring force) position in meters, x is the joint position in meters, f is the spring force in Newtons and k is the spring constant in N/m. Note that joint damping exists within the PrismaticJoint itself, and so is not included here.

Note: This is different from the LinearSpringDamper: this PrismaticSpring is associated with a joint, while the LinearSpringDamper connects two bodies.

Template Parameters

T	The scalar type, which must be one of the default scalars.

#include <drake/multibody/tree/prismatic_spring.h>

Public Member Functions
	PrismaticSpring (const PrismaticJoint< T > &joint, double nominal_position, double stiffness)
	Constructor for a linear spring attached to the given prismatic joint.
	~PrismaticSpring () override
const PrismaticJoint< T > &	joint () const
	Returns the joint associated with this spring.
double	nominal_position () const
double	stiffness () const
T	CalcPotentialEnergy (const systems::Context< T > &context, const internal::PositionKinematicsCache< T > &pc) const override
	(Advanced) Calculates the potential energy currently stored given the configuration provided in context.
T	CalcConservativePower (const systems::Context< T > &context, const internal::PositionKinematicsCache< T > &pc, const internal::VelocityKinematicsCache< T > &vc) const override
	(Advanced) Calculates and returns the power generated by conservative force elements or zero if this force element is non-conservative.
T	CalcNonConservativePower (const systems::Context< T > &context, const internal::PositionKinematicsCache< T > &pc, const internal::VelocityKinematicsCache< T > &vc) const override
	(Advanced) Calculates the rate at which mechanical energy is being generated (positive) or dissipated (negative) other than by conversion between potential and kinetic energy.
Does not allow copy, move, or assignment
	PrismaticSpring (const PrismaticSpring &)=delete
PrismaticSpring &	operator= (const PrismaticSpring &)=delete
	PrismaticSpring (PrismaticSpring &&)=delete
PrismaticSpring &	operator= (PrismaticSpring &&)=delete
Public Member Functions inherited from ForceElement< T >
	ForceElement (ModelInstanceIndex model_instance)
	Default constructor for a generic force element.
	~ForceElement () override
ForceElementIndex	index () const
	Returns this element's unique index.
void	CalcAndAddForceContribution (const systems::Context< T > &context, const internal::PositionKinematicsCache< T > &pc, const internal::VelocityKinematicsCache< T > &vc, MultibodyForces< T > *forces) const
	(Advanced) Computes the force contribution for this force element and adds it to the output arrays of forces.
	ForceElement (const ForceElement &)=delete
ForceElement &	operator= (const ForceElement &)=delete
	ForceElement (ForceElement &&)=delete
ForceElement &	operator= (ForceElement &&)=delete
Public Member Functions inherited from MultibodyElement< T >
virtual	~MultibodyElement ()
ModelInstanceIndex	model_instance () const
	Returns the ModelInstanceIndex of the model instance to which this element belongs.
template<typename = void>
const MultibodyPlant< T > &	GetParentPlant () const
	Returns the MultibodyPlant that owns this MultibodyElement.
void	DeclareParameters (internal::MultibodyTreeSystem< T > *tree_system)
	Declares MultibodyTreeSystem Parameters at MultibodyTreeSystem::Finalize() time.
void	SetDefaultParameters (systems::Parameters< T > *parameters) const
	Sets default values of parameters belonging to each MultibodyElement in parameters at a call to MultibodyTreeSystem::SetDefaultParameters().
void	DeclareDiscreteState (internal::MultibodyTreeSystem< T > *tree_system)
	Declares MultibodyTreeSystem discrete states.
void	DeclareCacheEntries (internal::MultibodyTreeSystem< T > *tree_system)
	(Advanced) Declares all cache entries needed by this element.
bool	is_ephemeral () const
	Returns true if this MultibodyElement was added during Finalize() rather than something a user added.
void	set_is_ephemeral (bool is_ephemeral)
	(Internal use only) Sets the is_ephemeral flag to the indicated value.
	MultibodyElement (const MultibodyElement &)=delete
MultibodyElement &	operator= (const MultibodyElement &)=delete
	MultibodyElement (MultibodyElement &&)=delete
MultibodyElement &	operator= (MultibodyElement &&)=delete

Friends
template<typename U>
class	PrismaticSpring

Additional Inherited Members
Protected Member Functions inherited from ForceElement< T >
virtual void	DoDeclareForceElementParameters (internal::MultibodyTreeSystem< T > *)
	Called by DoDeclareParameters().
virtual void	DoSetDefaultForceElementParameters (systems::Parameters< T > *) const
	Called by DoSetDefaultParameters().
Protected Member Functions inherited from MultibodyElement< T >
	MultibodyElement ()
	Default constructor made protected so that sub-classes can still declare their default constructors if they need to.
	MultibodyElement (ModelInstanceIndex model_instance)
	Constructor which allows specifying a model instance.
	MultibodyElement (ModelInstanceIndex model_instance, int64_t index)
	Both the model instance and element index are specified.
template<typename ElementIndexType>
ElementIndexType	index_impl () const
	Returns this element's unique index.
template<typename ElementOrdinalType = int64_t>
ElementOrdinalType	ordinal_impl () const
	Returns this element's unique ordinal.
const internal::MultibodyTree< T > &	get_parent_tree () const
	Returns a constant reference to the parent MultibodyTree that owns this element.
const internal::MultibodyTreeSystem< T > &	GetParentTreeSystem () const
	Returns a constant reference to the parent MultibodyTreeSystem that owns the parent MultibodyTree that owns this element.
void	SetTopology ()
	(Internal use only) Gives MultibodyElement-derived objects the opportunity to set data members that depend on topology and coordinate assignments having been finalized.
virtual void	DoDeclareDiscreteState (internal::MultibodyTreeSystem< T > *)
	Implementation of the NVI DeclareDiscreteState().
virtual void	DoDeclareCacheEntries (internal::MultibodyTreeSystem< T > *)
	Derived classes must override this method to declare cache entries needed by this element.
systems::NumericParameterIndex	DeclareNumericParameter (internal::MultibodyTreeSystem< T > *tree_system, const systems::BasicVector< T > &model_vector)
	To be used by MultibodyElement-derived objects when declaring parameters in their implementation of DoDeclareParameters().
systems::AbstractParameterIndex	DeclareAbstractParameter (internal::MultibodyTreeSystem< T > *tree_system, const AbstractValue &model_value)
	To be used by MultibodyElement-derived objects when declaring parameters in their implementation of DoDeclareParameters().
systems::DiscreteStateIndex	DeclareDiscreteState (internal::MultibodyTreeSystem< T > *tree_system, const VectorX< T > &model_value)
	To be used by MultibodyElement-derived objects when declaring discrete states in their implementation of DoDeclareDiscreteStates().
systems::CacheEntry &	DeclareCacheEntry (internal::MultibodyTreeSystem< T > *tree_system, std::string description, systems::ValueProducer value_producer, std::set< systems::DependencyTicket > prerequisites_of_calc)
	To be used by MultibodyElement-derived objects when declaring cache entries in their implementation of DoDeclareCacheEntries().
bool	has_parent_tree () const
	Returns true if this multibody element has a parent tree, otherwise false.

Constructor & Destructor Documentation

◆ PrismaticSpring() [1/3]

template<typename T>

PrismaticSpring ( const PrismaticSpring< T > & )

delete

◆ PrismaticSpring() [2/3]

template<typename T>

PrismaticSpring ( PrismaticSpring< T > && )

delete

◆ PrismaticSpring() [3/3]

template<typename T>

PrismaticSpring	(	const PrismaticJoint< T > &	joint,
		double	nominal_position,
		double	stiffness )

Constructor for a linear spring attached to the given prismatic joint.

Parameters

[in]	nominal_position	The nominal position of the spring x₀, in meters, at which the spring applies no force. This is measured the same way as the generalized position of the prismatic joint.
[in]	stiffness	The stiffness k of the spring in N/m.

Exceptions

std::exception if stiffness is (strictly) negative.

◆ ~PrismaticSpring()

template<typename T>

~PrismaticSpring ( )

override

Member Function Documentation

◆ CalcConservativePower()

template<typename T>

T CalcConservativePower	(	const systems::Context< T > &	context,
		const internal::PositionKinematicsCache< T > &	pc,
		const internal::VelocityKinematicsCache< T > &	vc ) const

overridevirtual

(Advanced) Calculates and returns the power generated by conservative force elements or zero if this force element is non-conservative.

This quantity is defined to be positive when the potential energy is decreasing. In other words, if PE is the potential energy as defined by CalcPotentialEnergy(), then the conservative power, Pc, is Pc = -d(PE)/dt.

See also: CalcPotentialEnergy(), CalcNonConservativePower()

Implements ForceElement< T >.

◆ CalcNonConservativePower()

template<typename T>

T CalcNonConservativePower	(	const systems::Context< T > &	context,
		const internal::PositionKinematicsCache< T > &	pc,
		const internal::VelocityKinematicsCache< T > &	vc ) const

overridevirtual

(Advanced) Calculates the rate at which mechanical energy is being generated (positive) or dissipated (negative) other than by conversion between potential and kinetic energy.

Integrating this quantity yields work W, and the total energy E = PE + KE - W should be conserved by any physically-correct model, to within integration accuracy of W.

See also: CalcConservativePower()

Implements ForceElement< T >.

◆ CalcPotentialEnergy()

template<typename T>

T CalcPotentialEnergy	(	const systems::Context< T > &	context,
		const internal::PositionKinematicsCache< T > &	pc ) const

overridevirtual

(Advanced) Calculates the potential energy currently stored given the configuration provided in context.

Non-conservative force elements will return zero.

Parameters

[in]	context	The context containing the state of the MultibodyTree model.
[in]	pc	A position kinematics cache object already updated to be in sync with context.

Precondition: The position kinematics pc must have been previously updated with a call to CalcPositionKinematicsCache().

Returns: For conservative force models, the potential energy stored by this force element. For non-conservative force models, zero.

See also: CalcConservativePower()

Implements ForceElement< T >.

◆ joint()

template<typename T>

const PrismaticJoint< T > & joint ( ) const

Returns the joint associated with this spring.

Exceptions

std::exception if this element is not associated with a MultibodyPlant.

◆ nominal_position()

template<typename T>

double nominal_position ( ) const

◆ operator=() [1/2]

template<typename T>

PrismaticSpring & operator= ( const PrismaticSpring< T > & )

delete

◆ operator=() [2/2]

template<typename T>

PrismaticSpring & operator= ( PrismaticSpring< T > && )

delete

◆ stiffness()

template<typename T>

double stiffness ( ) const

◆ PrismaticSpring

template<typename T>

template<typename U>

friend class PrismaticSpring

friend

The documentation for this class was generated from the following file:

drake/multibody/tree/prismatic_spring.h

Detailed Description

Public Member Functions

Friends

Additional Inherited Members

Constructor & Destructor Documentation

◆ PrismaticSpring() [1/3]

◆ PrismaticSpring() [2/3]

◆ PrismaticSpring() [3/3]

◆ ~PrismaticSpring()

Member Function Documentation

◆ CalcConservativePower()

◆ CalcNonConservativePower()

◆ CalcPotentialEnergy()

◆ joint()

◆ nominal_position()

◆ operator=() [1/2]

◆ operator=() [2/2]

◆ stiffness()

Friends And Related Symbol Documentation

◆ PrismaticSpring